Pressure sensitive copying paper

ABSTRACT

A pressure sensitive copying paper is prepared using a color former of the general formula   WHEREIN R1 and R2 each represents an alkyl group having 1 to 5 carbon atoms or a benzyl group, and X1, X2, X3 and X4 each represents a hydrogen atom, a halogen atom, an alkoxyl group or a methyl group. The compound of the above general formula is incapsulated in solution and the thus formed microcapsules are applied to an upper paper. When this upper paper is superimposed over a lower paper coated with an electron acceptable solid acid such as an acid clay, in such a manner that the microcapsule coated surface is in direct contact with the acid coated surface, and pressure applied thereto, a deep reddish purple color is formed in those areas to which pressure has been applied. The color former of the above general formula may also be admixed with yellow orange, or blue color formers to produce black images.

United States Patent 54] PRESSURE SENSITIVE COPYING PAPER 2 Claims, No Drawings [5 2] US. Cl 117/361, ll7/36.9, 260/3305 [51] Int. Cl 841m 5/22 [50] Field ofSearch ll7/36.2,

[56] References Cited UN lTED STATES PATENTS 3,49l,ll6 l/l970 Lin ll7/36.2 3,499,902 3/l970 Coles et al. l l7/36.2 3,509,l74 4/l970 Lin l l7/36.8

Primary Examiner-Murray Katz A!t0rneySughrue. Rothwell. Mion, Zinn & Macpeak ABSTRACT: A pressure sensitive copying paper is prepared using a color former of the general formula wherein R and R each represents an alkyl group having I to 5 carbon atoms or a benzyl group, and X,, X X and X each represents a hydrogen atom, a halogen atom. an alkoxyl group or a methyl group. The compound of the above general formula is incapsulated in solution and the thus formed microcapsules are applied to an upper paper. When this upper paper is superimposed over a lower paper coated with an electron acceptable solid acid such as an acid clay, in such a manner that the microcapsule coated surface is in direct contact with the acid coated surface, and pressure applied thereto, a deep reddish purple color is formed in those areas to Y which pressure has been applied. The color former of the above general formula may also be admixed with yellow orange, or blue color formers to produce black images.

The present invention relates to a pressure sensitive copying paper and more particularly to a pressure Sensitive copying paper in which color formers are used.

Ordinary pressure sensitive copying papers are-classified into two types. the first of which comprises a combination of a so-called upper paper and a lower paper. The uppenpaper is prepared by applying to a surface of a support microcapsules containing an organic solvent solution of a substantially colorless organic compound having electron donating and color forming properties (hereinafter referred to as color former). The lower paper is prepared by applying -an electron acceptable solid acid to a surface of another support. If desired. an intermediate paper prepared byapplying a solid acid to a surface of a support and microcapsules containing a color former to the other surface thereof may be employed. The second type of copying paper consists of a support which has been coated with both 'a solid acid and microcapsules (as mentioned above) to a surface of a support.

In using the first type of paper comprising the combination of an upper paper and a lowerpaper or the combination of -an upper paper, an intermediate paper and -a lower papent'hey are superimposed in such -a manner that the microcapsule layer and solid acid layer come into contact with each other.

When a localized pressure is applied to the combination,= the microcapsules present in the area under pressure are 'broken. and the color former liberated from the microcapsules reacts with the solid acid to form a color dye. Similarly-in the caseof using a pressure sensitive copying paper of the type having the microcapsules and solid acid on the samesurface ofthe 'support. the paper forms color dye in the areas to which pressure is applied.

Hitherto, there has not been known any colorless compound which by itself will form a reddish purple color onreaction with an electron acceptor. However as substantially colorless compounds which will by themselves form magenta color on reaction with an electron acceptor there are known Rhodamine B-Anilinolactam and Rhodamine B-P- Chloroanilinolactam as disclosed in US. Pat. NO. 2.695.245. These compounds, however. are slow in colorforming speed and have poor fastness to light after color-forming. -A s compounds which are initially yellow and instantly develop magenta there are known Rhodamine-B-P-nitroanilinolactam as disclosed in US. Pat. NO 2,695,245 and 2-(4-N,N- diethylaminostyryl)-3,3-dimethyl-3H-indole as disclosed in Japanese Pat. No. 2 l033/ 1966. but these are poor in fastness to light. both before and after color-fonning.

An object of the present invention is to provide a pressure sensitive copying paper which will form a reddish purple color by incorporating into the microcapsule the compound represented by the general formula set out below.

Another object of the present invention is to provide apressure sensitive copying paper which will form black. blue-black or other desired hues by combination of the compound described below with any of the known yellowish -oran'ge-or blue color formers.

We have found that by using a compound represented by the general formula (wherein R -an'd Rgeach represents an 'a'lltyl' group having one to five carbon atoms or-a' benz'yl group.-and X.. X Xyand 'X. each represents a hydrogen atom. ahalogenatom; an rilkoxyl group. or a'methyl group); as acolo'r formei'i' there isolatained -a pressure sensitive-copying paper which will f0ll11 'a reddish purple color. or by combination 'withany of the known' yellowishorange 'or' blue'colofformers." Wilf'form'black. blue black=orother desired-hue. The 'pressuresen'sitive copying paper containing a compound of the la'bovejgeneral formula in accordance withthe presentinventio'n'hasa very higli stability in airbefore color forming. and consequently. does :not

- discolor and does not loseits color forming property during storage: -lt-in'stantly-1"orms the deep reddish purple colorand is very excellentin -fastness' to li'ghwheat' resistance an'd water resistance after'colonformingz ln addition; it is not 'r'lesen'sitized by admixture with the 'known yellowish orange or blue color developers.

The compound-representedby the abo've general form u'la which will form reddish purple'co'lorisexemplified by the following compounds:

other absorption bond for carbonyl and hydroxyl groups is observed. The results of the elementary analysis .coincide with the theoretical values as indicated by the following examples in which the manufacture of typical compounds represented by the above general formula is illustrated.

SYNTHESIS EXAMPLE 1 ybenzoyU-benzoic acid and 9.7 g. (l/21 mole) of 6-ethoxythioindoxyl were dissolved in 30 g. of a 96 percent sulfuric acid at a temperature below 40 C. and reacted at (9032) C. for 3 hours. After being cooled to room temperature. the liquid reaction mixture was poured into 500 g. of ice water and the precipitate was separated by filtration. The precipitate was then extracted with 300 cc. of chloroform while neutralizing with an aqueous caustic soda. The resulting chlorofonn solution was washed several times with water and condensed under reduced pressure. and the thus precipitated crystal was recrystallized from a solution in a mixture of benzene and ligroin to obtain 18.6 g. of a colorless crystal having a melting point of 194-196 C A max 570mg. (95 percent acetic acid).

The crystal had the following composition: C,,H,,O,NS C; 71.31 (71.24). H:5.34(5.36).

The numerical values outside the parentheses are the measured values and those within parentheses are the theoretical values in percent. The data of elementary analysis is sir'hilarly indicated in the following examples.

SYNTHESIS EXAMPLE 2 Manufacture of the color developer (2). R.=R =Et. X.=Me. X EH and X =C1 in the general formula.

15.7 g. 1/21 mole) of 2-(4'-diethylamino-2'-hydroxybenzoyl)-benzoic acid and 9.9 g. l/2l mole) of 6-chloro-4- methylindoxyl were reacted and treated in the same manner as in example 1. and the precipitate was recrystallized with acetone to obtain 17.8 g. of a colorless crystal having a meltmg point of 234-235 C.. Amax=573 m;t(95 percent acetic acid).

The crystal had the following composition:

C H O NSCL C; 68.13 (6821). H; 4.66 (4.63). N; 2.94

SYNTHESIS EXAMPLE 3 Manufacture of the color developer (3). R,=Me. R =benzyl. X =X,=Cl and X,=X,=H in the general formula.

18.1 g. (1/21 mole) of 2-(4N-benzyl-N-methylamino-2'- hydroxy-benzoyl) benzoic acid and l 1.0 g. l/20 mole) of4.7- dichlorothio-indoxyl were dissolved in 40 g. of a 90 percent sulfuric acid at a temperature below 40 C. and thereafter reacted at (95:2) C. for 4 hours and treated in the similar manner as in example 1 to obtain 21.4 g. of a colorless crystal having a melting point of 224-226 C.. Amax=574mp.( 95 percent acetic acid).

The crystal had the following composition:

c,.,t-i,,o.Nsc|, C; 68.70 (68.58). H; 3.65 (3.53). N;

SYNTHESIS EXAMPLE 4 Manufacture of the color developer (4). R,=Et. R,=benzyl. X,=X==H. X,=Cl and X.=Me in the general formula.

18.8 g. (l/21 mole) of 2-(4N-benzyl-N-ethylamino-2'- hydroxy-benzoyl) benzoic acid and 9.9 g. (l/20 mole) of 5- chloro-7-methyl-thioindoxyl were treated in the similar manner as in example 1 to obtain 19.3 g. of a colorless crystal having a melting point of 203-205" C.. krnax=573 mp.( 95 percent acetic acid).

The crystal had the following composition:

C,,H,.O,NSC1 C; 71.42 (71.51). H; 4.49 (4.42). N; 2.60

SYNTHESIS EXAMPLE 5 Manufacture of the color developer (5). R,=Et. R,=benzyl. X,=X,=X,=X.=H in the general formula.

18.8 g. (l/20 mole) of 2-(4'-N-benzyl-N-ethylamino-2'- hydroxyl-benzoyl) benzoic acid and 7.4 g. (l/20 mole) of thioindoxyl were dissolved in 41 g. of a percent sulfuric acid at a temperature below 40C.. then reacted at (:2 C. for 3 hours and treated in the similar manner as in example 1 to obtain 17.5 g. of a colorless crystal having a melting point of 166168 C.. Amax=57 2 mp.( percent acetic acid).

The crystal had the following composition:

C H O NS C; 76.07 (76.14), H; 4.73 (4.80). N; 286

(2.81 For the manufacture of pressure sensitive copying papers .using as a color former the compound represented by the general formula in accordance with the present invention. there may be adopted such methods well known in the art as disclosed in US Pat. Nos. 2.548.366. 2.800.457. and 2.800.458. i.e.. the method of preparingmicrocapsules making use ofthe phenomenon of complex coacervation.

The present invention is characterized by the use of the compound represented by the above general formula as a color former. and the characteristics of the pressure sensitive copying paper in accordance with the present invention are not varied significantly by the method employed for the manufacture thereof.

The color former may be used in the amount of 0.5 to 5 percent by weight ofthe organic solvent.

The electron acceptive solid acid used in the pressure sensitive copying paper in accordance with the present invention includes a clay substance such as acid clay, active clay, atapalgite, zeorite or bentonite, and solid organic acid, such as succinic acid, tannic acid, pyrogallol, pentachlorophenol or phenolic resin. The organic solvent for dissolving the color former includes ethylene glycol, chlorinated benzenes and chlorinated diphenyls.

Some embodiments of the present invention will now be illustrated by the following examples in which there were used compounds represented by the above general formula as color formers.

EXAMPLE 1 3 g. each of the color formers l to 5 was separately dissolved in 100 g. of trichlorodiphenyl, and 20 g. of gum arabic, and 160 g. of water added to and the resulting solution emulsified at 50 C.

To the emulsion thus obtained there were added 20 g. of an acid-treated gelatin and 160 g. of water, then added thereto with stirring, acetic acid to adjust the pH of the emulsion to 5. To the emulsion there was then added 500 g. of water to promote coacervation and, after formation of a film of a concentrated liquid gelatin-gum arabic mixture around each particle of the trichlorodiphenyl containing the color former dissolved therein, the pH ofthe emulsion was adjusted to 4.4, and 3.8 g. of a 37 percent formalin was added to the emulsion to harden said liquid film on the particles of trichlorodiphenyl. Thereafter, the emulsion was cooled to l C., added with an aqueous sodium hydroxide to adjust its pH to 9 allowed to stand still for -6 hours to complete capsulization. The encapsulated liquid mixture was then applied to a paper by, e.g., roll coating, air knife coating or like coating manner and dried. When the coated paper thus obtained (upper paper) was superimposed on a paper which had been coated with an electron acceptive solid acid such as acid clay, active clay, atapalgite, georite. or bentonite in the manner such that the coated surface of the upper coated came into contact with the coated paper of the clay-coated paper and a hand-writing pressure or impact pressure of a typewriter key was imposed thereto, a deep color was instantly fonned on the pressed areas of the lower clay coated paper. The color formed was reddish purple in all cases regardless of the particular color former and clay used. The thus formed color faded little when exposed to direct sunlight for a long period of time, and faded little when wetted with water. Similar reddish purple color forming was also attained in the case where there was used a lower paper coated with an organic solid acid such as succinic acid, pyrogallol. para-toluenesulfonic acid, pentachlorophenol or phenolic resin in place of the clays. No deterioration in color forming property was observed even where the upper papers thus obtained were heated at 100 C. for hours or exposed to sunlight for a long period of time.

EXAMPLE 2 An upper paper was prepared in the same manner as in example 1 except that there was used 1.0 g. of the color former (2) in combination with 0.5 g. of Benzoyl Leuco Methylene Blue, 0.7 g. Malachite Green Lactone, 0.3 g. of Crystal Violet Lactone, and 1.2 g. of 2-(4-acetamidostyryl)-3,3-dimethyl- 3H-indole all of which are well-known color formers. There was instantly formed black color on the lower paper when the upper paper thus formed was superimposed on the lower paper having been coated with an electron acceptive sold acid and a handwriting pressure was imposed thereto.

A pressure-sensitive copying paper obtained by treating a paper in the same manner as in example I except that there was used 0.7 g. of the color former (l) in combination with 0.5 g. of Benzoyl Leuco Methylene Blue, 2.0 g. of Chrystal Violet Lactone, and 0.3 g. 2-(4-acetamidostyryl-3,3-dimethyl- 3H-indole. There was instantly formed a blue black color on the lower paper when the upper paper thus formed was superimposed on the lower paper having been coated with an electron acceptive solid acid and a hand-writing pressure imposed thereto.

EXAMPLE 4 The encapsulated liquid mixture as in example 1 was applied to a clay-coated paper. The pressed areas of the dualwherein R, and R each represents a member selected from the group consisting of an alkyl group having one to live carbon atoms and a benzyl group, and X,, X X and X each represents a member selected from the group consisting of a hydrogen atom, a halogen atom, an alkoxy group and a methyl group which in coming into contact with an electron acceptable solid acid forms a color dye.

2. The pressure sensitive copying paper as claimed in claim I wherein said electron acceptable solid acid is a member selected from the group consisting of acid clay, active clay, attapalgite, zeolite. bentonite, succinic acid, tannic acid. pyrogallol, pentachlorophenol and phenolic resin. 

2. The pressure sensitive copying paper as claimed in claim 1 wherein said electron acceptable solid acid is a member selected from the group consisting of acid clay, active clay, attapalgite, zeolite, bentonite, succinic acid, tannic acid, pyrogallol, pentachlorophenol and phenolic resin. 